Assembler - simple Calculator

Hello,
i wanted to start a small project in assembler since i'm going to study computer sience soon and a friend told me we'd need to do assembler in the first semester~
Since i'm still pretty noobie, i wanted to ask if it's possible for somebody to help me with this. Generally i don't even know where to start, so some tutorials may be good or some source codes. A finished Calculator code would do as well, then i could just look up which funktion does what and so on ^^
I also want to mention that my english may not be as good as yours, so please try to explain something as simple as possible.

Greetings, Kanaria

Edit: Forgot to mention that i've got a 8051 processor and it has 3 buttons. (: